One-Rep Max Calculator

Enter the weight you lifted and how many reps you completed to estimate your one-rep max (1RM). The tool averages three proven formulas and gives a percentage-of-1RM table for programming your sets.

Enter the weight and reps, then press Estimate 1RM.

How a one-rep max is estimated

Your one-rep max (1RM) is the most weight you can lift for a single repetition. Testing it directly is risky, so lifters estimate it from a lighter set taken close to failure. The most-cited formula is Epley:

1RM = weight × (1 + reps ÷ 30)

This calculator also applies the Brzycki formula (weight × 36 ÷ (37 − reps)) and the Lombardi formula (weight × reps^0.10), then averages them, because each is a little more accurate in different rep ranges.

Worked example

You lift 185 lb for 5 reps:

Epley: 185 × (1 + 5 ÷ 30) = 185 × 1.167 ≈ 216 lb.
Brzycki: 185 × 36 ÷ 32 ≈ 208 lb.
Estimated 1RM: averaging the formulas lands around 210–216 lb.

Using the percentage table

Strength programs prescribe loads as a percentage of 1RM: roughly 100% for 1 rep, 95% for 2, 90% for 4, 85% for 6, 80% for 8, and so on. The calculator turns your estimate into a ready-to-use table so you can pick a working weight for any rep target. Estimates are most accurate at 10 reps or fewer — beyond that, fatigue and technique make the math less reliable. Always warm up, use a spotter and treat the number as a guide, not a guarantee.

Tip: dialling in nutrition around training? See the TDEE calculator for maintenance calories and the macro calculator for protein, carbs and fat.

Frequently asked questions

How accurate is an estimated 1RM?

For sets of about 10 reps or fewer, the formulas are usually within a few percent of a tested max. Accuracy falls as reps climb, because fatigue and form drift make a high-rep set a weaker predictor of a true single.

Which formula is best?

No single formula wins everywhere. Epley tends to read high at low reps, Brzycki reads low at high reps. Averaging Epley, Brzycki and Lombardi — as this tool does — gives a balanced estimate across the common rep ranges.

How do I use the percentage table?

Pick the rep target for your set and read off the suggested weight. For example, a hypertrophy day at 8 reps uses roughly 80% of your 1RM; a heavy single uses close to 100%.

Should I actually test my 1RM?

Only when you're experienced, well warmed up and have a spotter. For most people an estimate from a 3–5 rep set is safer and accurate enough to program training without the injury risk of a true max attempt.

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Mustafa Bilgic · Editor, Calcool
Averages the Epley, Brzycki and Lombardi 1RM formulas. Educational — warm up and use a spotter. Everything runs in your browser — nothing you enter is uploaded, logged or stored.

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